The present invention relates to a golf ball having different colors in an inner part of a dimple and the land part thereof, and relates to a method for manufacturing the golf ball.
Japanese Patent Application Publication No. 60-34469 and Japanese Patent Application Publication No. 05-111550 describe a method for manufacturing a golf ball having different colors in an inner part of a dimple and the land part thereof, in which method, after the entire surface of the golf ball has been colored by painting, the surface of the land part is ground to remove the paint on the land part.
Usually, a golf ball is formed by using a forming mold capable of being divided into two pieces, which mold has a spherical cavity therein, is formed with a large number of protrusions for forming dimples (dimple forming protrusions) on the wall surface of the cavity, and has a parting line substantially at the position of the equator of the cavity. On the parting line, gates for injecting a cover material for the golf ball are provided at equal intervals on the circumference. Therefore, for the golf ball formed by using such a mold, burrs are produced on the parting line. The burrs are removed by grinding the surface of the golf ball after the golf ball has been formed by using the mold.
Japanese Patent Application Publication No. 60-34469 describes a method in which the golf ball is color painted after being formed by using the mold and before burrs are removed. In this method, unfortunately, unpainted portions and unevenly painted portions are produced by the influence of burrs. Therefore, this method has a problem of difficulty in evenly color painting the entirety of the golf ball.
Japanese Patent Application Publication No. 05-111550 describes a method in which the golf ball is color painted after the burrs have been removed by grinding. In this method, unfortunately, when the burrs on the parting line are removed by grinding, the surface of the golf ball cannot be ground uniformly due to the burrs. In particular, land part portions at the edges of dimples near the parting line are undesirably ground at the same time. Therefore, even if the entirety of the golf ball is thereafter color painted and the surface of the land part is ground, it is difficult to remove the paint in the land part portion, which has been scraped off by the grinding of burrs, thoroughly by grinding because the land part portion having been scraped off by the grinding of burrs is lower than other land parts, which poses a problem that the dimple color remains in some of land parts.
Japanese Patent Application Publication No. 11-114092 describes a method in which protrusions are formed in the land parts at both ends of the dimple along the parting line, whereby, when the burrs on the parting line are ground, the surface of the golf ball can be ground uniformly by the plurality of protrusions, so that excessive grinding of the land part portion at the edge of the dimple is avoided.